Multi-stage polymer as a grinding additive and a method of producing the same

A multi-stage polymer comprising, based on the total weight of the multi-stage polymer, from 1 wt. % to 99 wt. % of a first stage polymer, and from 1 wt. % to 99 wt. % of a second stage polymer,

• wherein the first stage polymer comprises, as polymerization units, based on the total weight of the first stage polymer:
• (a) from 2 wt. % to 20 wt. %, of a nonionic macromonomer, characterized by the following formula:
• H2C═C(R)CO2(CH2CH2O)n(CH(R′)CH2O)mR″, wherein R is H or CH3, R′ is C1-C2 alkyl;
• R″ is C8-C30 alkyl, C8-C16 alkylphenyl or C13-C36 aralkylphenyl;
• n is an integral number from 6 to 100 and m is an integral number from 0 to 50, provided that n≧m and m+n is from 6 to 100;
• (b) from 35 wt. % to 60 wt. %, of an α,β-ethylenically unsaturated carboxylic acid monomer;
• and
• (c) from 35 wt. % to 60 wt. %, of an α,β-ethylenically unsaturated nonionic monomer;
• wherein the first stage polymer has a weight average molecular weight of at least 50,000 Daltons;
• and
• the second stage polymer comprises, as polymerization units, based on the total weight of the second stage polymer:
• (e) from 10 wt. % to 70 wt. %, of an α,β-ethylenically unsaturated carboxylic acid monomer;
• and
• (f) from 30 wt. % to 90 wt. %, of a nonionic α,β-ethylenically unsaturated monomer;
• wherein the second stage polymer has a weight average molecular weight of from 500 to 20,000 Daltons, and the second stage polymer contains a substantial absence of the nonionic macromonomer.